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The earthquake hazard alert of September 1982 in Southern Tobago

F. D. MORGAN^*, G. WADGE, J. LATCHMAN, W. P. ASPINALL, D. HUDSON and F. SAMSTAG

SEISMIC RESEARCH UNIT UNIVERSITY OF THE WEST INDIES, ST. AUGUSTINE, TRINIDAD
DEPARTMENT OF GEOPHYSICS TEXAS A&M UNIVERSITY, COLLEGE STATION, TEXAS 77843
INSTITUTE OF MARINE AFFAIRS, P.O. BOX 3160, CARENAGE, TRINIDAD

Abstract

An earthquake swarm that occurred in the vicinity of the island of Tobago (West Indies) during the latter half of 1982 was monitored in the near-field by a five-station seismograph network. The monitoring of the swarm eventually led to the issuing of a potential earthquake hazard alert, 3 days prior to the major energy release (earthquake magnitude m_b = 5.2). We discuss the reasons for issuing this alert. In particular, daily monitoring of the changing b value and energy release was used to constrain estimates of future earthquake behavior. The aftershock seismicity showed activity in a direction trending west to WNW. This is in good agreement with the focal mechanism of the main earthquake which showed right-lateral strike-slip motion along an E-W fault plane dipping steeply (71°) to the north. This active fault appears to form part of the previously unrecognized Southern Tobago Fault System for which there is evidence in the geology of the Late Neogene rocks of the island.

Footnotes

^* Present address: Department of Geophysics, Texas A & M University, College Station, Texas 77843.

Present address: NERC Unit for Thematic Information Systems, Department of Geography, University of Reading, Reading RG6 2AB, United Kingdom.

Present address: Principia Mechanica Ltd., 50 Vineyard Path, London SW14 8ET, United Kingdom.

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